Seismic exploration involves surveying subterranean geological formations for hydrocarbon deposits. A seismic survey typically involves deploying seismic source(s) and seismic sensors at predetermined locations. The sources generate seismic waves, which propagate into the geological formations creating pressure changes and vibrations along their way. Changes in elastic properties of the geological formation scatter the seismic waves, changing their direction of propagation and other properties. Part of the energy emitted by the sources reaches the seismic sensors. Some seismic sensors are sensitive to pressure changes (hydrophones), others to particle motion (e.g., geophones), and industrial surveys may deploy only one type of sensors or both. In response to the detected seismic events, the sensors generate electrical signals to produce seismic data. Analysis of the seismic data can then indicate the presence or absence of probable locations of hydrocarbon deposits.
Marine seismic surveys may be carried out in a variety of manners. For example, towed array surveys are quite popular and involve the use of one or more large vessels towing multiple seismic streamers and sources. Streamers can be over 10 km long and contain a large number of closely spaced hydrophones and possibly also particle motion sensors, such as accelerometers.
Another method for acquiring seismic data involves the deployment of seismic nodes at the seafloor. Such nodes may contain a pressure sensor, a vertical geophone and two orthogonal horizontal geophones as well as a data recorder and battery pack. Nodes may be deployed by an ROV or simply deployed off the back of a ship.